Three hundred parliamentarians from Britain, France and Germany have called on the US Congress not to let President Trump abandon the Iran deal, warning it would undermine the very concept of diplomacy and any future negotiations.

The letter, written by British MP Richard Bacon and his German and French counterparts, Omid Nouripour and Delphine O, was published in the Guardian on Thursday. In it, they argue that the deal has been the only effective control of Tehran’s nuclear ambitions, and has helped prevent an arms race and a potentially devastating conflict in the Middle East.